The present invention relates to actuators and more particularly to actuators utilised within gas turbine engines in order to vary blade or vane or nozzle tab configuration.
Use of shape memory materials such as shape memory alloys is well known in order to achieve variation in dimensions or actuation by such deformation. Typically, the shape memory alloy or material acts against a bias in the form of a mechanical spring. An example of a prior use of shape memory materials is given in U.S. Pat. No. 6,813,877 in relation to nozzle tabs and fins adjustable dependent upon exit temperatures from a gas turbine engine.
Generally, a spacing pedestal must be provided between the shape memory alloy or material. The spacing pedestals secured to the shape memory alloy create stress rising features and so do not allow the full potential of the shape memory material deformation to be utilised for actuation. By increasing the potential working area per unit volume of the shape memory material, greater performance can be achieved whilst providing a more uniform stress distribution, which in turn should increase operational life and/or loading.
Previous approaches have generally implied a necessity to achieve a two dimensional design and loading structure whilst certain situations require a three dimensional application such as changing an air flow direction or aperture size so that consideration must be made to utilisation of a faster design which in turn is less efficient.